Secondary batteries are widely pervasive as power supplies for portable equipment such as a portable telephone, a digital camera, a laptop computer, etc., a power supply for a vehicle and a household power supply. The secondary battery is configured such that a battery element (electrode laminated body) formed by winding or laminating a positive electrode and a negative electrode while the positive electrode and the negative electrode are spaced from each other across a separator is contained and enclosed together with electrolyte in an outer container. In the secondary battery, a sufficient amount of electrolyte must be impregnated into cavity portions of the electrode laminated body inside the outer container. When the amount of impregnated electrolyte is small, a coating on the surface of the electrode becomes non-uniform, resulting in generation of a deposit on the surface of the electrode or the like, so that electrochemical characteristics such as a cycle characteristic, etc. are degraded and the desired battery characteristics cannot be obtained.
Patent Document 1 discloses a method of injecting electrolyte into an outer container while a pressure is not particularly changed in an atmospheric pressure environment, and, after the injection of the electrolyte, reducing a pressure in the outer container to a pressure which is lower than the atmospheric pressure, but is equal to or higher than the vapor pressure of the electrolyte, thereafter sealing an injection port (opening portion) of the outer container.
Patent Document 2 discloses a method of injecting electrolyte into an outer container housing an electrode laminated body therein in an environment which is almost vacuum due to pressure reduction, and after the injection of the electrolyte, pressurizing an inside of the outer container to impregnate the electrolyte into the electrode laminated body.
Patent Document 3 discloses a method of starting injection of electrolyte into an outer container under a negative pressure environment of about 10 kPa (a pressure of about one tenth of the atmospheric pressure) achieved by reducing pressure from the atmospheric pressure, and completing the injection of the electrolyte before or at the time when nearly a state of vacuum is reached by continuing the pressure reduction.